This invention relates in general to fluid pumps and more specifically to a peristaltic pump having a cam driven plurality of fingers for sequentially engaging a resilient tube to create liquid flow through the tube.
Conventional linear and rotary peristaltic pumps typically have a section of resilient tubing positioned between a wall and a set of rollers or reciprocating pushers that progressively compress sections of the tubing to pump liquids. Such pumps are often used in medical applications, such as intravenous infusion or withdrawing fluids such as in a wound drainage system. These pumps operate in a positive manner and are capable of generating substantial outlet pressures.
Typical linear peristaltic pumps include those described by Sorg et al. in U.S. Pat. No. 2,877,714, Borsannyi in U.S. Pat. No. 4,671,792 Heminway et al. in U.S. Pat. No. 4,893,991 and Canon in U.S. Pat. No. 4,728,265. While generally effective, these pumps are large, complex and cumbersome, requiring a drive shaft parallel to a resilient tube and a plurality of cams along the drive shaft to move pushers toward and away from the tube.
Rotary peristaltic pumps generally dispose a resilient tube along a circular path, with a number of rollers mounted around the circumference of a circular rotor sequentially rolling along the tube to occlude the tube and force liquid through the tube. Typical of such pumps are those disclosed by Soderquist et al. in U.S. Pat. No. 4,886,431 and Kling in U.S. Pat. No. 3,172,367. These pumps often have relatively low efficiency and impose high shear and tension stresses on the tube causing internal tube wall erosion or spallation. The tube may eventually be permanently deformed so that the tube becomes flattened into a more oval shape and carries less liquid.
Another type of peristaltic pump has a tube arranged along a circular path with a cam member within the circle sequentially moving a plurality of blunt pushers or fingers outwardly to sequentially compress the tube from one end of the path to the other. Typical of these pumps are those shown by Gonner in German Patent No. 2,152,352 and Tubospir in Italian Patent No. 582,797.
These pumps tend to be less complex than linear peristaltic pumps. However, the pressure imposed by the blunt fingers reduces tube life, sometimes causing internal tube wall erosion or spallation, which results in particulate matter getting into the fluid stream. Tube with different wall thicknesses cannot be accommodated by these pumps, since with thinner than standard tubes the fingers will not properly occlude the tube and with thicker than standard tubes the tube will close prematurely and be subject to excessive compression, requiring higher cam drive power and causing excessive wear on the cam and tube.
Thus, there is a continuing need for peristaltic pumps of greater simplicity, small size, low drive power requirements and which can accommodate resilient tubes of varying wall thickness while reducing wear and internal erosion of the resilient tube.